Role of Nutrients in Producing the Growth Inhibitory Effect on Bacteria in UV-irradiated Water

Abstract

UV disinfection is considered as a useful disinfection process. In application to water treatment, residuality of its germicidal effect needs to be evaluated. In this study, two groups of water samples were prepared with different compositions of nutrients and three levels of concentrations of nutrients. All samples contain both photosensitizing organic matter and ferric ion. These water samples were tested to produce growth inhibitory effect after UV irradiationand its effect was evaluated by reduction of E. coli. Water samples were irradiated by medium-pressure UV lamp to produce 1600m Ws/cm² just before inoculating exponentially growing E. coli., whose survival was determined for 48 hours by colony forming assay. Up to 2.0 log reduction of E. coli. was observed in the UV irradiated water containing nonutrients, and the reduction was enhanced up to 3.3 log by addition of nutrients. Among the added nutrients, nitrate ionand sodium glycerophosphate enhanced the reduction of E. coli. In the three levels of nutrients concentrations tested, maximum reduction of E. coli. was observed at the following concentrations: 0.05g/l of Sodium Glycerophosphate, 0.1g/l of KNO₃, 0.15g/l of Ca (NO₃) ₂, 0.04g/l of MgSO₄. The UV energy absorbed in the water was not related well to thereduction of E. coli.